## LESSWRONGLW

It's simpler than you think: you just treat i as an unknown variable where all you know is that i^2 = -1. Then if you want to, say, multiply together two complex numbers, it's all the algebra you're already familiar with: (a + bi)(c + di) = ac + adi + bci + bdi^2 = ac - bd + (ad + bc)i. That's it - that's all the complex maths you need to follow the QM sequence.

To better understand why it is used imagine a map, going right is +, going left is -, going up is i, going down is -i. Turning left is multiplying by i, turning right is multiplying by -i. So i is used to calculate things where you need 2 dimensions.

3Kaj_Sotala8yAlright, thanks.

# How accurate is the quantum physics sequence?

1 min read17th Apr 201268 comments

# 49

Prompted by Mitchell Porter, I asked on Physics StackExchange about the accuracy of the physics in the Quantum Physics sequence:

What errors would one learn from Eliezer Yudkowsky's introduction to quantum physics?

Eliezer Yudkowsky wrote an introduction to quantum physics from a strictly realist standpoint. However, he has no qualifications in the subject and it is not his specialty. Does it paint an accurate picture overall? What mistaken ideas about QM might someone who read only this introduction come away with?

I've had some interesting answers so far, including one from a friend that seems to point up a definite error, though AFAICT not a very consequential one: in Configurations and Amplitude, a multiplication factor of i is used for the mirrors where -1 is correct.

Physics StackExchange: What errors would one learn from Eliezer Yudkowsky's introduction to quantum physics?